1. Field of the Invention
This invention relates to a carriage running control system, and more particularly to a system for controlling running of carriages each having a device for communicating information with memory media installed on the ground such that, when a preceding carriage remains in a predetermined zone of a running track, a succeeding carriage is prevented from entering that zone.
2. Description of the Related Art
It has been conventional practice in an assembly line of automobile bodies or electric appliances to transport parts and unfinished products automatically by means of a plurality of carriages running on a predetermined running track with a guideline laid therealong. Generally, each of such carriages has an ultrasonic sensor to avoid striking a preceding carriage from behind.
However, this sensor usually is a directional sensor and therefore incapable of detecting a preceding carriage in a curved portion of the running track. The sensor also has the disadvantage of being vulnerable to disturbances.
To compensate for the inability of the directional sensor, a presence monitoring zone is provided in a curved portion or the like of the running track to detect any preceding carriage lying in the monitoring zone. If there is a preceding carriage in the monitoring zone, control is effected to prevent a succeeding carriage from entering the monitoring zone to avoid a rear-end collision. Japanese Patent Publication Kokai No. 1991-31062, for example, discloses a control system including detectors disposed at an entry end and an exit end of a presence monitoring zone for detecting passage of carriages, and a main controller installed on the ground for receiving detection results from the detectors and determining whether a carriage is present in the monitoring zone or not. The carriages communicate with the main controller at the entry end of the presence monitoring zone to obtain information as to whether the monitoring zone may be entered.
However, the above system involves a high equipment cost in that the detectors must be installed at two positions, i.e. the entry end and exit end of a presence monitoring zone, and these detectors must be wired to the main controller. Further, the main controller has a heavy burden with an increased number of jobs to be processed.
On the other hand, a carriage control system has been developed recently which includes rewritable memory media called ID tags installed at positions just short of stopping points, branching points and the like of carriages. The memory media store running control information such as distances to the stopping points and post-branching addresses. Each carriage has a communicating device for communicating with the storage media without making a physical contact therewith, to read the control information from the media. In this way, while running along the tracks, the carriages obtain running information as necessary at the positions where the memory media are installed.